The present invention relates to an analogue method for calibrating the initial sensitivity of the non-destructive flaw-detecting apparatus, especially the eddy current roll-flaw detecting apparatus, and to a non-destructive flaw-detecting apparatus, especially an eddy current roll-flaw detecting apparatus, whose initial sensitivity can be calibrated by the method.
In a rolling mill, the roll is the main consumable part. After being used for a period of time, cracks and hardness abnormalities (hereinafter referred to collectively as xe2x80x9cflawxe2x80x9d) may occur on the surface of the roll, which, if not found and repaired in good time, may cause serious spalling of the roll body or even break the roll. Generally, to prevent such a case from happening, the roll is regularly detected by means of an eddy current roll-flaw detecting apparatus. The conventional eddy current roll-flaw detecting apparatus comprises an impedance analyzing unit, a modulation analyzing circuit and a warning circuit. In order to effectively detect the flaws of the roll, the initial sensitivity of the eddy current roll-flaw detecting apparatus should be calibrated. CN 1114747 A (laid open on Jan. 10, 1996) disclosed such a calibrating method, comprising the following steps: detecting an artificial defect sample by means of a computer-based eddy current flaw detector to obtain a first vector; attaching the detecting probe of the computer-based eddy current flaw detector to the output terminal of an analogue artificial defect signal generator to obtain a second vector, and adjusting the attenuator and the phase shifter of the analogue artificial defect signal generator in such a way that the second vector equals the first vector; attaching the output terminal of the analogue artificial defect signal generator to the probe of the eddy current roll-flaw detecting apparatus, and adjusting the modulation frequency of the analogue artificial defect signal generator and the gain of the eddy current roll-flaw detecting apparatus to enable it to give a warning.
The disadvantage of the above known method for calibrating the initial sensitivity of the eddy current roll-flaw detecting apparatus is that the precision of calibration is low. This is because the detecting means used in the calibration procedure is different from that used in actual detection; in the former case, a computer-based eddy current flaw detector which is separated from the eddy current roll-flaw detecting apparatus is used and, in the latter case, the impedance analyzing unit built in the eddy current roll-flaw detecting apparatus is used. The output powers of the two detecting means are different and the impedances of them can not be matched easily.
The object of the invention is to provide a method for calibrating the initial sensitivity of the eddy current roll-flaw detecting apparatus with high precision, and an eddy current roll-flaw detecting apparatus, whose initial sensitivity can be calibrated by the method.
According to the invention, the method for calibrating the initial sensitivity of the eddy current roll-flaw detecting apparatus comprises the following steps: a) detecting an artificial defect sample to obtain a first vector; b) generating an analogue artificial defect signal; c) adjusting the analogue artificial defect signal to make it equal the first vector; and d) inputting the analogue artificial defect signal, which has been adjusted, into the eddy current roll-flaw detecting apparatus, and adjusting the eddy current roll-flaw detecting apparatus to enable it to give a warning, wherein steps a) and c) are both implemented by means of the impedance analyzing unit having the function of displaying the impedance vector built in the eddy current roll-flaw detecting apparatus.
The eddy current roll-flaw detecting apparatus according to the invention comprises: an impedance analyzing unit having the function of displaying the impedance vector, thereby displaying the first vector and the analogue artificial defect signal; a modulation analyzing circuit; and a warning circuit.
In accordance with the method of the invention, the same detecting means, i.e., the impedance analyzing unit as one of the components of the eddy current roll-flaw detecting apparatus, is used in both of the calibration procedure and actual detection. Therefore, the disadvantage of the prior art caused by the use of two different detecting means as stated above can be overcome, and a much higher precision of calibration can be achieved.
Since the impedance analyzing unit of the eddy current roll-flaw detecting apparatus of the invention has the function of displaying impedance vectors, the initial sensitivity of the apparatus can be calibrated by the method of the invention. Therefore, the precision of detection of the apparatus of the invention can be increased enormously.